Method of inhibiting acid corrosion of ferrous metals

#This invention relates generally to acid corrosion inhibitors and in particular to corrosion inhibitors useful in oil field treating operations. In one aspect the invention relates to a method of using a substituted quaternary compound as an acid corrosion inhibitor. In another aspect the invention relates to the use of an aqueous acid solution containing a substituted quaternary compound.

#In the acid treatment of subterranean formations penetrated by a wellbore, an aqueous acid solution is injected down the well into the formation to dissolve formation materials and/or other materials deposited in the wellbore thereby improving permeability of the formation and its production. The acid treatment may be carried out under matrix injection rates or fracturing rates.

#A serious problem associated with acidizing formations is the high corrosivity of the acid solution on surface and subsurface metal equipment. The acid, normally HCl or mud acid (HCl-HF mixture), is highly corrosive to ferrous metals. Accordingly, the acid treatment almost always involves the use of corrosion inhibitors.

#The preferred method for carrying out the present invention involves incorporating a small but effective amount of the quaternary corrosion inhibitor in an aqueous acid solution for treatment of subterranean formations. The aqueous acid solution includes solutions of hydrochloric acid (HCl), mud acid (a mixture of hydrochloric acid and hydrofluoric acid), acetic acid and formic acid. Although sulfuric acid is not normally used in the petroleum industry, it is used in pickling operations and therefore is included herein. All of these acids are highly corrosive to ferrous metals and therefore require inhibition. The concentration of the corrosion inhibitor should be sufficiently high to inhibit corrosion of the ferrous metals and normally will range from 0.01 to 10 percent (preferably 0.05 to 3.0 %) by volume based on the combined volume of the inhibitor and acid solution. The inhibitor concentration in a particular treatment will depend on several factors including acid type and concentration, temperature, exposure time, and the presence of other additives. It is important that the inhibitor be added to the acid as early as possible to protect storage, pumping and handling equipment, as well as tubular goods in the well.

#The quaternary compound, as mentioned above, is the reaction product of a tertiary aromatic heterocyclic amine and a (halo substituted aryl) alkyl halide, having the following formula. ##STR2## wherein ARYL is a heterocyclic aromatic ring or rings; N.sup.+ is a positively charged nitrogen atom and is part of AHYL; ARYL' is an aromatic ring or rings; and R is an alkyl group containing from 1 to 3 carbon atoms and connects N.sup.+ to ARYL'; X is a halogen; Y is a halogen substituted on ARYL'; and Z is a halogen or hydrogen substituted on ARYL'.

#The preferred quaternary compound is selected from the group consisting of: ##STR3## wherein R is an alkyl group containing from 1 to 3 carbon atoms; X and Y are halogens; and Z is a halogen or hydrogen.